The SA propulsion system incorporates air-breathing Ejector Ramjet engines, instead of the conventional rocket motors used on other space launch vehicles. In the past, ramjet engines have been used in classified hypersonic vehicle programs. Typical ramjet engines will only operate at very high speeds and therefore need to be boosted to their operational speed by the use of an alternate propulsion system, e.g. conventional jet engines, rockets, or separate aircraft. SA has overcome this limitation by developing a patented ejector system that enables ramjet engines to operate at low speeds, including even static condition, without degrading their performance at hypersonic speeds.

The SA ejector ramjet is seven times more fuel-efficient than the best rocket engines. Ramjet engines breathe oxygen from the atmosphere, so the oxidizer weight doesn't have to be carried onboard the vehicle as is necessary with rocket-powered vehicles. This air breathing characteristic, along with the high energy density of the ramjet's liquid hydrogen fuel, results in a significant reduction in overall vehicle volume and mass. This allows the vehicle to accelerate more rapidly and achieve exoatmospheric conditions with reduced energy expenditure.

Additionally, liquid hydrogen is an environmentally friendly propellant because hydrogen combustion does not produce carbon emissions and hydrogen can be generated using clean, sustainable energy sources. The propulsion system combined with streamlined aerodynamics provides SA's reusable launch vehicle a tremendous advantage in reliability and operating cost.